Aziz has slammed opposition leaders as "villains" and "troublemakers".

He has described some as "dangerous Islamists, racist extremists and the leftovers of former regimes which brought the country to its knees".

Earlier this week, he accused Islamists of "just awaiting their political failure to take up arms".

That brought an indignant response from Jemil Ould Mensour of the Islamist party Tewassoul.

"It is Mr Aziz who took up arms against an elected regime and is assassinating democracy," he charged, referring to the 2008 coup.

Veteran opposition leader Ahmed Ould Daddah, who heads the Gathering for Democracy (RFD), has urged voters to make "the necessary leap to get rid of dictatorship and generalised bankruptcy".

Economic factors

The ruling Union for the Republic is campaigning largely on changes it made in the 2017 constitution, abolishing the senate and bringing in a new national anthem and flag.

Voters endorsed the controversial measures in a referendum, while the opposition warned they would give the president more power.

After more than a year of detention on corruption charges, former senator Mohammed Ould Ghadda, who led the campaign against the constitutional changes, was due to be released on Friday, his lawyer said.

However, Ould Ghadda rejected the conditions set for his release and remained in detention, laywer Mohamed El Mamy said in a statement.

On the economic front, authorities say growth has revived, with three percent reported in 2017 and a poverty rate of 31 percent, against over 40 percent in 2008.

The opposition sees a fall in living standards since the introduction at the start of the year of new, lower-value bank notes. National debt is equal to GDP.

Mauritania, which hosted an African Union summit in July, has recently revived diplomatic ties with Morocco, after years of tension over the status of Moroccan-annexed Western Sahara.

In July, a Mauritanian general took over the command of the G5 Sahel force as the army works with Burkina Faso, Mali, Niger and Chad in a European-backed military operation to defeat armed groups in the region.